The silicone is not the issue. The point Yuri has been making possibly
was the simple old principle that applies to any sealed cavity: somehow
water will get in, possibly quite slowly, and it may take a long time.
But once it is in there, it will start accumulating at the bottom, and
there is no effective way out. Two very common ways for water to get
into hermetically sealed cavities are condensation of air humidity on
the inside walls of the cavity, and breathing of the cavity due to
temperature and pressure changes. And either means that the water just
gets more and more over time... It just happens sometimes, in spite of
best materials and workmanship. Periodic inspections can make it worse,
as there always is a risk of damaging a seal. There are ways around it:
* Drain holes at the bottom (but if the pipe is buried in the ground
keep in mind that the holes may turn into artesian wells when the rain
saturates the soil).
* Ventilation / airflow - this is good for removing moisture, even if
sometimes a little bit of water gets in. Obvious drawback: dust and bugs
can get in, unless the intakes are filtered; but in that case you need
to replace filters periodically. Passive ventilation is fairly easy to
implement and has good long-term reliability. However, if the pipe is
long and thin and filled with cables it may not be sufficient to remove
all humidity.
* An automatic pump to remove any water once detected. Disadvantage:
long-term reliability may be questionable.
YMMV...
Kind regards,
Helmut.
On 22/01/14 10:24, Volker Kuhlmann wrote:
On Wed 22 Jan 2014 00:27:22 NZDT +1300, yuri wrote:
Since changing career from sparky to telco tech, I've learned a few things.
One of them is that all outdoor conduit will eventually fill up with
water, no matter how good you think you've waterproofed it.
I find it hard to believe that a good layer of silicone sealant will
last for less than 10 years. If you just stick the pipe pieces together,
sure, and I wouldn't assume that PVC pipe glue is watertight unless
there is assurance that all surfaces have been covered fully and are
resting wihtout gap against each other while the glue sets.
Outdoor rated grease-filled cat6 is a must if you're looking for a
long-term solution.
Maybe some single-mode and multi-mode fibre if you *really* want to
future-proof.
My really future proof solution fit for long term is to keep the pipes
accessible.
Volker
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